An ultrastructure study designed to elucidate the cellular morphology of the reproductive systems of Schistosoma mansoni, S. haematobium, S. japonicum and S. mattheei in unisexual, bisexual and cross infections. Following a study of spermatogenesis, oogenesis, vitellogenesis and egg-shell formation, as well as the cellular architecture of the vitelline gland duct, oviduct, ootype, Mehlis' gland, uterus, vas deferns, and seminal vesicle will be determined. Application of the results of this study will provide a means by which the effects of chemotherapeutic agents of reproduction and the formation of viable eggs can be assessed at a subcellular level.